Find me a device that works at 600Mhz everyday I use my N900 one or two hours per day. That means the clock gets higher than 250Mhz ONLY those hours. It runs mostly at 250Mhz with bursts (no more than 10-20mins) at 1150Mhz. I suppose my grandchildren will love it when I give it to them as a gift Just for the record, I have my N900 overlocked to 1.1Ghz since Lehto's kernels... Now I'm using Titan's. I've never experienced any problems, except some crashes which might not be related to OCing...
Oh dear where was your brain when you typed this lol. HEAT is the deciding factor here and the figures your quoting are simply not true in any way or form. I suggest you read that link properly and you might understand a bit more... good luck.